Influence of stage of lactation on glucose and glutamine metabolism in isolated enterocytes from dairy cattle

Abstract

Pathways of glutamine and glucose metabolism in early-, mid-, and late-lactation dairy cows were evaluated by in vitro incubations of enterocytes for 2 hours with [U- 14-C]glutamine and [U- 14C]glucose. Enterocytes from early-lactation cows produced greater amounts of CO 2 from glutamine in concentrations that ranged from 2 to 8 mmol/L than enterocytes from either mid- or late-lactation cows. Enterocytes from early-lactation cows also produced greater amounts of CO 2 from 4 and 6 mmol/L glucose than enterocytes from either mid- or late-lactation cows. Glutamine was metabolized via glutaminolysis mainly to ammonia, alanine, aspartate, glutamate, and CO 2, and more of these products were produced in enterocytes from early-lactation cows than from pooled mid- and late-lactation (PML) cows. Glucose was metabolized mainly to lactate, as compared with pyruvate and CO 2. Lactate and CO 2 production were both greater in enterocytes from early-lactation cows than from PML cows. Glutamine as the sole substrate accounted for all the energy requirements of enterocytes from early-lactation cows but contributed only 31% in the presence of glucose. Similarly, glucose accounted for all the energy requirements of enterocytes from early-lactation cows and contributed 69% in the presence of glutamine. In enterocytes from all cows, the rate of adenosine triphosphate (ATP) production was greater in the presence of both glucose and glutamine compared with that in the presence of either substrate alone. The rate of production of ATP from glucose as the sole substrate was two to three times greater than that obtained from glutamine as the sole substrate in enterocytes from all groups of cows. Thus, we suggest that although glutamine is an important energy source for enterocytes, it is not quantitatively as important as glucose as an energy source for enterocytes from lactating cows.